In a multi-carrier communication system, a base station controls data to be transmitted to each terminal through downlink and also controls data that each terminal transmits to the base station through uplink. The base station transmits control information to each terminal in order to control downlink/uplink data transmission. This control information is transmitted to the terminal through part of downlink resources.
The control of uplink/downlink data transmission at the base station can be referred to as scheduling and control of limited wireless resources for multiple terminals or services can be referred to as wireless resource scheduling. Wireless resource scheduling can be performed through actual unit resources used for data transmission. In this case, unit resources for scheduling at the base station and physical unit resources used for actual data transmission can be considered identical.
FIG. 1 illustrates an example of use of wireless resources in a multi-carrier system.
It can be seen from FIG. 1 that wireless resources of uplink and downlink, i.e., time-frequency resources, are used for data transmission. It can also be seen that downlink wireless resources are used not only for transmission of data but also for transmission of control information for controlling the downlink/uplink data transmission described above.
The terminal can receive downlink data by receiving control information transmitted from the base station through downlink wireless resources and obtaining information of wireless resources or the like of the data transmitted to the terminal through downlink wireless resources. The terminal can transmit uplink data by receiving control information transmitted from the base station through downlink wireless resources and obtaining information of wireless resources or the like of the data to be transmitted from the terminal to the base station through uplink wireless resources. Although not illustrated in FIG. 1, each terminal can also transmit control information through uplink wireless resources to notify the base station of its channel state, data receiving state, terminal state, etc.
Each receiving side of data can transmit an ACK/NACK signal for the data to notify the transmitting side whether or not the receiving side has normally received the data having been transmitted from a base station to a terminal through downlink or transmitted from a terminal to a base station through uplink.
More specifically, to increase the reliability of data communication, the receiving side transmits a positive acknowledgement (ACK) when the data has been received normally and transmits a negative acknowledgement (NACK) when the data has not been received normally.
The ACK/NACK signal occupies physical frequency and time resources since it is transmitted through downlink or uplink. When the terminal has transmitted an ACK/NACK signal through uplink in response to data transmitted from the base station through downlink, the base station needs to know the position of a resource through which the terminal has transmitted the ACK/NACK signal for the data. On the other hand, when the base station has transmitted an ACK/NACK signal, the terminal needs to know the position of a resource through which the ACK/NACK signal has been transmitted.